SYNTHETIC LIPOPEPTIDES INCORPORATED IN LIPOSOMES - IN-VITRO STIMULATION OF THE PROLIFERATION OF MURINE SPLENOCYTES AND IN-VIVO INDUCTION OFAN IMMUNE-RESPONSE AGAINST A PEPTIDE ANTIGEN

Amphiphilic lipopeptides, such as Pam(3)CysAlaGly and Pam(3)CysSerSer, were synthesized and incorporated into liposomes, and their ability t o induce the proliferation of BALB/c mouse splenocyte was tested in vi tro. When compared to monophosphoryl lipid A (MPL) the following poten cy order was found: liposomal lipopeptides > liposomal MPL > free (emu lsified) lipopeptides. These results strongly depend on the size of th e vesicles used: a mitogenic effect was observed only with lipopeptide s incorporated within vesicles of diameter less than or equal to 100nm while lipopeptides in larger vesicles (diameter approximate to 300 nm ) gave no response. This may be related to the necessity for the lipos ome-associated lipopeptides to be endocytosed to reach putative intrac ellular targets. As immunoadjuvanticity seems to be linked to B-lympho cyte activation, the lipopeptides represent attractive alternatives to MPL for the realization of completely synthetic liposome-based peptid e vaccine formulations. This was borne out by showing that Pam(3)CysAl aGly and Pam(3)CysSerSer, when incorporated in small unilamellar vesic les carrying a covalently conjugated synthetic peptide of sequence IRG ERA, corresponding to an epitope of the C-terminal region of histone H 3, were able to induce a potent and long-lasting immune response. (C) 1997 Elsevier Science Ltd.